Paint sprayer with dynamic pulse width modulation driven motor

ABSTRACT

A fluid sprayer includes a housing, a pump, a nozzle, a high voltage direct current (HVDC) brushed electric motor that drives the pump, and a motor controller electrically connected to the motor. The motor controller drives the motor with a high speed pulse width modulated (PWM) drive signal that switches current through the motor on and off. The motor controller varies the PWM signal as a function of a spray setting input and sensed current through the motor.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.62/446,487 filed Jan. 15, 2017 for “PAINT SPRAYER WITH DYNAMIC PULSEWIDTH MODULATION DRIVEN MOTOR” by Tyler J. Kruzel. The aforementionedU.S. Provisional Application No. 62/446,487 is hereby incorporated byreference in its entirety.

BACKGROUND

In most high voltage direct current brushed (HVDC) motor controllers inpaint sprayer applications, use silicon controlled rectifiers (SCRs) orTriacs due to their simplistic and inexpensive control design. In atypical application circuit of a design using an AC to DC rectifyingbridge and a Triac to drive a high voltage direct current (HVDC) brushedmotor. This motor control strategy yields very high peak currents, forexample, around 7.3 Arms (root mean square Amperes) that decay down to 0Arms valleys every 8.3 ms in a 120 VAC 60 Hz power distribution system.As a result, motor brush life can be negatively affected or impacted,and operation of the sprayer can be affected by motor thermal tripscaused by overheating.

SUMMARY

A fluid sprayer includes a housing, a pump, a nozzle, a high voltagedirect current (HVDC) brushed electric motor that drives the pump, and amotor controller electrically connected to the motor. The motorcontroller drives the motor with a high speed pulse width modulated(PWM) drive signal that switches current through the motor on and off.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a handheld paint sprayer.

FIG. 1B is a cross-sectional view of the handheld paint sprayer.

FIG. 2 is an electrical block diagram of the handheld paint sprayer.

FIG. 3 is a chart demonstrating different phases of operation of theelectric motor of the handheld paint sprayer.

DETAILED DESCRIPTION

In this disclosure a variable output single phase high voltage (HVDC)brushed motor controller for paint sprayers (or other fluid sprayers) isdescribed. This motor controller commutates a brushed motor that willdrive a pump in a paint sprayer. The motor controller eliminates motorthermal trips, increases the existing motor's brush life, and provideshigh resolution variable output adjustment for the painter. Thecontroller also increases motor efficiency to make it capable of drivingthree piston pump with low Arms.

Various embodiments of the present disclosure can be used to spray paintand/or other fluids and solutions. While paint will be used herein as anexemplar, it will be understood that this is merely one example and thatother fluids (e.g., water, oil, stains, finishes, coatings, solvents,etc.) can be sprayed instead of paint.

FIG. 1A is a perspective view, and FIG. 1B is a cross-sectional view ofsprayer 10. FIGS. 1A and 1B will be discussed together. Sprayer 10 shownin FIGS. 1A and 1B is a handheld paint sprayer that can be supported andoperated with just one hand during spraying. As shown in FIGS. 1A and1B, sprayer 10 includes housing 12 (which includes main body 14 andhandle 16), fluid supply system 18, spray tip assembly 20 (whichincludes nozzle 22), pump 24 (which includes pistons 26 and cylinders28), valves 30, motor 32, wobble drive 34, power cord 36, motorcontroller 38, spray setting input 40, and trigger 42.

It will be understood that this is but one type of sprayer within whichthe features of the present disclosure could be embodied. The featuresof the present disclosure could be practiced on larger, non-handheldsprayers. For example, the features of the present disclosure could beimplemented in a professional-grade floor unit.

Fluid supply system 18 is a reservoir that can be used to hold the paintto be sprayed, such as by holding the paint in a flexible polymercontainer. The paint is sprayed out of nozzle 22 of spray tip assembly20. Nozzle 22 can be a carbide orifice at the end of the fluid pathwaythat atomizes paint into a fan spray pattern for painting surfaces. Themechanism (pump 24, valves 30, motor 32, and wobble drive 34) forpumping the paint from the fluid supply system 18 and out nozzle 22 iscontained within main body 14 of housing 12. Housing 12 can be, forexample, a molded polymer clamshell.

Trigger 42 is located at an upper end of handle 16. When activated,trigger 42 causes sprayer 10 to spray paint, and when deactivatedtrigger 42 causes the sprayer 10 to stop spraying paint. While trigger42 is shown in this embodiment, it will be appreciated that other typesof inputs or activators can instead be used for commanding sprayer 10 tospray paint.

Sprayer 10 can develop different levels of pressure for expelling thepaint from nozzle 22 depending on spray setting input 40. Spray settinginput 40 can be a potentiometer dial, a digital input, slider, one ormore buttons, or other type of input. Generally, the user can turn thespray setting input 40 to a higher level for greater pressure and alower level for lower pressure. The flow of paint, and in particular thepattern of the atomized spray fan, is dependent on the fluid pressure.

Sprayer 10 receives AC input power from power cord 36, which connects toa conventional electrical wall outlet. The AC input power provides powerto motor 32 and motor controller 38 of sprayer 10. Motor controller 38can be entirely or partially mounted on a circuit board. Motorcontroller 38 controls operation of sprayer 10. In particular, motorcontroller 38 receives an on/off input from the trigger 42, a spraysetting from spray setting input 40, and AC power from power cord 36.Using these inputs, motor controller 38 controls operation of motor 32,which drives pump 24 through wobble drive 34.

Motor 32 is contained within main body 14 of housing 12. Motor 32 canbe, for example, a high voltage brushed DC electric motor. Rotationaloutput from motor 32 operates wobble drive 34 which converts therotational output into linear reciprocal motion. While a wobble drive 34is shown to convert rotational motion into linear reciprocal motion,alternative mechanisms can instead be used, such as various yokes and/orcranks.

The reciprocal motion is used to operate pump 24. Pump 24 includes ahousing within which pistons 26 reciprocate. While only one piston isshown in the view of FIG. 1B, in one embodiment two other pistons arelocated within pump 24 and operate similarly. However, differentembodiments may only have two pistons or a single piston (e.g.,non-handheld floor units can have a single, larger piston). Pistons 26are located at least partially within cylinders 28 of pump 24. Pistons26 and cylinders 28 can be formed from carbide, amongst other options.

The reciprocating motion of each piston 26 pulls paint from fluid supplysystem 18 through the intake channel 44 and then into a chamber formedby cylinder 28 and piston 26 on an upstroke (or back stroke), and thenexpels the paint under pressure from the chamber on the downstroke (orforward stroke). The paint passes through one or more valves 30. Underpressure from the pump 24, the paint flows to nozzle 22 for release asan atomized spray fan. In floor units, the paint may travel through aflexible hose after being placed under pressure by the pump and releasedthrough a separate mechanical gun to which the flow fluidly connects.

Preferably, sprayer 10 is responsive, consistent, reliable, andlightweight. However, these can be competing considerations. When a userpresses trigger 42 or otherwise activates motor 32, a fine atomizationof paint in an even fan pattern is expected to quickly be output (e.g.,within 100 milliseconds) and maintained for the duration of trigger pullof trigger 42. This requires that motor 32 accelerate very quickly. Asmaller motor is also preferred to reduce weight, but is less capable offast acceleration to high pressure. These competing demands risk severalcomplications, such as ring fire and overheating, which are furtherdiscussed herein.

FIG. 2 shows a block diagram of some of the circuitry of sprayer 10.FIG. 2 shows high voltage direct current (HVDC) brushed motor 32, powercord 36, motor controller 38, spray setting input 40, trigger 42, andtrigger sense circuit 42A. Motor controller 38 includes HVDC powersupply 50 (which includes rectifier circuit 52 and filter circuit 54),switch mode power supply 56, microcontroller 58, pulse width modulation(PWM) driver 60, semiconductor switch 62, flyback diode 64, currentfeedback circuit 66 (which includes current sense resistor 68), andpressure sensor 70.

Motor controller 38 is powered by standard line (or mains) powerreceived from power cord 36 (e.g., a 120 volt 60 Hertz AC, or a 230 volt50 Hertz AC, or other regionally standard line power). The AC power frompower cord 36 is converted to a DC voltage of, for example, 165 volts,by HVDC power supply 50. Rectifier circuit 52 receives the AC power frompower cord 36 and full wave rectifies the power to produce rectifiedpower. Filter circuit 54 conditions or smoothes the rectified power tocreate, the DC voltage (e.g. 165 volts) that is supplied to terminal M1of motor 32.

Switch mode power supply 56 receives rectified power from HVDC powersupply 50 and generates supply voltages V1 and V2. All of the voltagesshare a common ground in the circuitry shown in FIG. 2. Supply voltageV1, which in one embodiment is 15 VDC, is used by PWM driver 60 toproduce a PWM drive signal that turns semiconductor switch 62 on andoff. Supply voltage V2, which in one embodiment is 3.3 VDC, powersmicrocontroller 58, spray setting input 40, trigger sense circuit 42A,PWM driver 60, and current feedback circuit 66.

Microcontroller 58 receives inputs from spray setting input 40, triggersense circuit 42A, and current feedback circuit 66. Based upon thoseinputs, microcontroller 58 outputs a PWM command signal to PWM driver60. In one embodiment, the PWM command signal has a frequency of 16 kHzfor in rush current during a starting sequence and a frequency of 32 kHzfor steady state current during a steady state phase of sprayeroperation. Microcontroller 58 determines the duty cycle of the commandsignal, and thus the on and off time of the semiconductor switch 62based upon the phase of operation, a spray setting input, and sensedcurrent.

The PWM drive signal from PWM driver 60 is supplied to semiconductorswitch 62, which is shown in FIG. 2 as an isolated gate bipolartransistor (IGBT). IGBT switch 62 has a control electrode (gate), afirst main current carrying electrode (collector), and a second maincurrent carrying electrode (emitter). IGBT switch 62 turns on and off inresponse to the PWM drive signal received at its gate.

Motor terminal M2 is connected to the collector of IGBT switch 62. Theemitter of IGBT switch 62 is connected to current sense circuitry 66.Flyback diode 64 is connected in parallel with motor 32. The anode offlyback diode 64 is connected to motor terminal M2, and the cathode offlyback diode 64 is connected to motor terminal M1.

When IGBT switch 62 is turned on, a current path is established throughmotor 36, IGBT switch 62, and current sense resistor 68 to ground. TheHVDC voltage at motor terminal M1 causes current to flow through motor32 to motor terminal M2, from collector to emitter of IGBT switch 62 andthrough current sense resistor 68. When IGBT switch 62 is turned off,the HVDC voltage is still present at motor terminal M1, but current flowthrough, IGBT switch 62 is interrupted. Flyback diode 64 conducts motorcurrent from terminal M2 back to terminal M1 when IGBT switch 62 turnsoff.

Microcontroller 58 can include, among other things, a digital processorand memory storing program instructions thereon which, when executed bythe processor, perform the functions described herein. Themicrocontroller 58 calculates and outputs the high speed pulse widthmodulation (PWM) command signal to PWM driver 60 to set a duty cycle forpowering motor 32. More specifically, motor 32 is powered not by acontinuous direct current but rather by a rapid series of voltage pulses(e.g., 165 volts DC). Each pulse is part of a cycle having an “on”portion and an “off” portion. The pulses are modulated in width(duration) over the cycle to deliver a greater or lesser amount ofenergy to motor 32 to increase or decrease the speed of motor 32. Foreach cycle, the duty or “on” portion can be expressed as a percentage ofthe cycle. The duty cycle in this sense ranges from 0% (no on pulse) to100% (pulse on fully throughout the cycle). Microcontroller 58 outputsthe PWM command signal to PWM drive 60, which provides the PWM drivesignal to the gate of IGBT switch 62 to cause the IGBT 64 to turn on andoff according to the frequency and duty cycle established by the PWMcommand signal. Specifically, IGBT Switch 64 turns on when the dutycycle is on (corresponding to pulse delivery to motor 32) and turns offwhen the duty cycle is off (corresponding to no pulse delivery to motor16). Flyback diode 64 bridges the motor 16 to freewheel during the offportion of the duty cycle while blocking potentially damaging voltagegenerated by the motor 32.

In operation, trigger 42 is activated (e.g., pulled), which causestrigger sense circuit 42A to signal microcontroller 58 to output the PWMcommand signal to PWM driver 60 to cause IGBT switch 62 to turn on andoff at the commanded frequency and duty cycle to cause current flowthrough motor 32.

The duty cycle of the PWM command signal may be calculated bymicroprocessor 58 before or while being output based on various inputs.Microcontroller 58 receives a signal from the spray setting input 40(such as a potentiometer) which is set to indicate a pressure, motorspeed, or other parameter setting desired by the user. In some cases,the duty cycle of the PWM command signal is based on the signal receivedby microcontroller 58 from the spray setting input 40 indicating theparameter setting. For example, a higher setting of the spray settinginput 40 can correspond to a user desire for greater fluid pressureoutput from pump 24 (which requires a correspondingly higher duty cycleto cause a higher motor 32 speed), while a lower setting of spraysetting input 40 can correspond to a user desire for lesser fluidpressure output from pump 24 (which requires a correspondingly lowerduty cycle to cause a lower motor 32 speed).

Additionally or alternatively to the trigger 42 and trigger sensecircuit 42A, the sprayer 10 can include a pressure sensor 70 which canbe a pressure transducer or pressure switch (e.g., in non-handheldversions) that measures the pressure anywhere along the fluid linebetween the output of the pump 24 and the nozzle 22. Microcontroller 58could start delivering the PWM command signal to PWM driver 60 to startmotor 32 when the pressure within the fluid line, as indicated by thepressure sensor 70, falls below a low pressure threshold. Likewise,microcontroller 58 could stop delivering the PWM command signal to PWMdriver 60 to stop motor 32 when the pressure within the fluid line, asindicated by the pressure transducer, rises above a low pressurethreshold. As alternatives to stopping and starting, microcontroller 58could increase or decrease the duty cycle of the PWM command signal toincrease or decrease pressure to maintain a preferred levelcorresponding to spray setting input 40. Fluid may be released from thefluid line (e.g., as an atomized spray) when a mechanical valve in thefluid line opens, thereby lowering the pressure and triggeringmicrocontroller 58 to turn on (or accelerate) motor 32 as described. Thethreshold(s) may be dynamically set based on the spray setting inputsignal to the microcontroller 58 from spray setting input 40.

Current flowing through motor 32 can cause several problems. If thecurrent and voltage are too high, then instances of ring fire can occurwherein current arcs between the trailing edge of the brush and therotating commutator of motor 32, which significantly reduces brush lifeor creates a short circuit around the commutator. Also, excessivecurrent through motor 32 generates heat, particularly on startup whenmotor 32 is accelerating. Higher heat can raise the coefficient offriction of the brush, increasing wear. Heat rise can also trip internalthermal fuses of motor 32 or other components. Once a motor thermal tripoccurs, the user has to wait until the motor cools down (which may be onthe order of 30 minutes) before spraying can be resumed. Variousfeatures are provided to limit ring fire and heat rise, as furtherdiscussed herein.

Current feedback circuit 66 monitors current through current senseresistor 68 and provides a current feedback signal to microcontroller58. In steady state operation, microcomputer 58 uses the currentfeedback signal in conjunction with the spray setting input signal and aproportional and integral control loop algorithm to keep the peak andRMS current through the motor 32 at or below a predetermined currentlevel. That current level can be at or just below the maximum continuousRMS current the motor 32 can handle without overheating (which due tothe benefits achieved using the techniques of the present disclosure canbe materially higher than the maximum continuous RMS current for whichthe motor 32 is rated). Current feedback circuit 66 includes currentsense resistor 68, which produces a current sense voltage as in functionof current from IGBT switch 62 that flows through current sense resistor68 to ground. The current feedback signal provided by current feedbackcircuit 66 to microcontroller 58 is based on the current sense voltage.Microprocessor 58 calculates the length of on time for each PWM cycle tomaintain adequate RMS current at or below the predetermined currentlevel. The microcontroller 58 may be programmed to increase or decreasethe duty cycle (on time) to maintain the current through the motor 32 ator near the predetermined current level. In one embodiment,microcontroller 58 is programmed to maintain the current at a first Armslevel during steady state operation such that the duty cycle isincreased if the current falls below the first Arms level by apredetermined amount (e.g. 0.1 Arms) and the duty cycle is decreased ifthe current rises above the first Arms level by a predetermined amount(e.g. 0.1 Arms). In some cases, the predetermined current level may onlyfunction as upper limit so as to limit the duty cycle when the currentexceeds the predetermined current limit but not otherwise increase theduty cycle based on a measured current. Alternatively, the set level canbe, for example, in a range between a low Arms level and a high Armslevel. Modulating the duty cycle to limit excessive current may beparticularly useful when motor 32 is already accelerated to a functionalspeed for spraying, but a greater level of current is typically neededon startup to accelerate motor 32. Mitigation of the previouslymentioned issues during startup are further discussed herein.

FIG. 3 shows a chart demonstrating different phases of operation formotor 32 driven by a pulse width modulated signal corresponding to thepulse width modulation command signal output by the microcontroller 58.Duty cycle level 80 indicates the programmed duty cycle across variousphases P1-P5 of the pulse width modulation command signal. First-fourthphases P1-P4 are different parts of a startup sequence while fifth phaseP5 is a steady state phase of indefinite duration (i.e. as long astrigger 42 is pulled). First-fourth phases P1-P4 of the startup sequenceare repeated for each trigger 42 pull or other activation of motor 32from a dead stop. Specifically, first-fourth phases P1-P4 of the startupsequence are intended to accelerate motor 32 from a stopped condition toa fully or nearly fully accelerated condition (e.g., accelerated to thespeed corresponding to the setting of the spray setting input 40).

The first phase P1 is a kick start phase in which a relatively high dutycycle pulse train is delivered to motor 32. Motor 32 is typically not inmotion during first phase P1, or at least at the start of phase P1, butthe pulses during phase P1 begin to establish the electromagnetic fieldthat will drive motor 32. The duty cycle may be constant at a firstlevel throughout first phase P1. The first level may be greater than85%. The first level may be greater than 90%. The first level may begreater than 92%. Moreover, the first level may be less than 100%, andin some cases may be less than or equal to 96%. The first level may bewithin the range 90-96%. The first level may be 95%. First phase P1 maybe less than 10, or 5, or 2 milliseconds (but greater than zero) induration. In some cases, first phase P1 is between 0.01-2.0milliseconds. In some cases, first phase P1 is 1.0 millisecond.

The current through motor 32 during first phase P rapidly increases, andmay be 20 Arms or higher by the end of first phase P1. This trajectoryfor current level would be too high to continue, as higher current risksring fire, excessive heat generation, and demagnetizing motor 32.Therefore, the duty cycle is decreased by microcontroller 58 for secondphase P2. Second phase P2 may be considered a wave shaping phase becausethe decrease in duty cycle decreases the current level profile throughmotor 32, transitioning from an increasing trajectory at the end offirst phase P1 to a leveling off or decaying trajectory soon after thestart of second phase P2.

The duty cycle during the second phase P2 is maintained below the dutycycle level of first phase P1. As shown, the duty cycle during secondphase P2 changes throughout phase P2. Specifically, the duty cycle rampsup, in this case linearly. The duty cycle during second phase P2 maystart out as less than 80%, 75%, or 70%, but greater than 50%, 55%, 60%,or 65%. The duty cycle during second phase P2 may start out as between60-70%. The duty cycle during second phase P2 may start out as 66%. Theduty cycle during second phase P2 may end at less than 95%, 90%, or 85%,but greater than 70%, 75%, 80%, or 85%. The duty cycle during the secondphase P2 may end at between 85-95%. The duty cycle during second phaseP2 may end at 92%. Second phase P2 may be longer than first phase P1.Second phase P2 may be greater than 5 or 8 milliseconds but less than 20or 15 milliseconds. In some cases, second phase P2 is between 9-11milliseconds. In some cases, the second phase P2 is 10 milliseconds.

Third phase P3 is a speed control phase in which the duty cycle isconstant at a predetermined level. The current through motor 32 is selflimited to some degree because motor 32 has accelerated, although not tofull speed, and motor 32 continues to accelerate through third phase P3.The current through motor 32 is used more efficiently for accelerationwork in this phase and results in less heat generation. The duty cyclein the third phase P3 is constant through third phase P3. The duty cycleduring third phase P3 may be less than the duty cycle of first phase P1.The duty cycle during third phase P3 may be greater than 90%, or 85%.The duty cycle in third phase P3 may be greater than 90% and less than100%. The duty cycle during third phase P3 may be 92%. Third phase P3may be longer than first phase P1. Third phase P3 may be the sameduration as second phase P2. Third phase P3 may be greater than 5 or 8milliseconds but less than 20 or 15 milliseconds. In some cases, thirdphase P3 is between 9-11 milliseconds. In some cases, third phase P3 is10 milliseconds. It is noted that second and third phases P2, P3 couldbe combined (or third phase P3 eliminated) such that the duty cycleincreases (e.g., linearly) through both phases with the starting andending duty cycle levels discussed in connection with second phase P2.

The duty cycle through fourth phase P4 is based on the spray settinginput 40. For example, if the user has input a setting that correspondswith 50% duty cycle (i.e. 50% power), then microcontroller 58 causes theduty cycle to be 50% throughout fourth phase P4. As such, the duty cyclethrough fourth phase P4 is variable based on user input. However, ringfire and overheating are still concerns at this phase, and therefore theduty cycle has an upper limit regardless of the current spray settinginput 40 setting. The upper limit can be 95%, or 92%. As such, if theuser set the current spray setting input 40 setting to a level whichwould correspond to 97% duty cycle, then the duty cycle for fourth phaseP4 would be the upper limit (e.g., 92%), not 97%. Fourth phase P4 may belonger than any of the first, second, or third phases P1, P2, P3(individually or collectively). Fourth phase P4 may be greater than 20,30, or 50 milliseconds but less than 85, 90, or 100 milliseconds. Insome cases, Fourth phase P4 is between 75-85 milliseconds. In somecases, fourth phase P4 is 82 milliseconds. It is expected that motor 32may not be spinning at a speed which corresponds to the steady statespeed for the setting provide by spray setting input 40 at the beginningof fourth phase P4, but it is expected that motor 32 will be spinning atthat speed by the end of fourth phase P4. In some embodiments, theduration of fourth phase P4 may be dependent on the acceleration ofmotor 32 or a feedback parameter. For example, microprocessor 58 mayonly transition from fourth phase P4 to fifth phase P5 when motor 32speed reaches a level that corresponds with the setting from currentspray setting input 40 or when the current through motor 32 is at orcrosses a threshold level.

Phase P4 could be longer than 100 ms in other embodiments, such asembodiments using a slightly larger motor or a motor that cannot handleas much current, or a drive and pump system with more mass. In thoseembodiments, it could take longer to fully accelerate the motor & drivesystem to sprayable pressures.

Fifth phase P5 corresponds to a steady state phase in which the PWMcommand signal is modulated based on the setting from current spraysetting input 40 and the predetermined current level. In some cases, thecurrent duty cycle will be set at whichever of the current spray settinginput 40 setting and the predetermined current level dictates a lowerduty cycle at the particular moment. In some cases, the duty cycle willbe maintained at the current spray setting input 40 as long as thepredetermined current level is within acceptable limit(s), but if thesensed current is beyond the predetermined current level (e.g., over athreshold, such as the first Arms level or outside a Arms range), thenmicrocontroller 58 will reduce or otherwise change the duty cycle torestore the level of the current through motor 32 to the predeterminedcurrent level. If the current level through motor 32 is within thepredetermined current level, then microcontroller 58 bases the dutycycle on the current spray setting input 40 setting until there is achange in the current level that deviates from the predetermined currentlevel. Limiting the duty cycle based on comparing the sensed currentthrough motor 32 (as represented by the current feedback signal fromcurrent feedback circuit 66) to the predetermined current level may onlybe implemented by microcontroller 58 in fifth phase P5, and accordinglymay not be performed in the first-fourth phases P1-P4. This is becausethe current will likely rise well above the predetermined current levelduring the startup sequence but should decay to, or below, thepredetermined current level by the end of the startup sequence.

Steady state phase P5 may extend indefinitely, until the trigger 42 orother activator is deactivated, at which point microcontroller 58discontinues the PWM command signal, which causes IGBT switch 62 toremain open and current through motor 32 to cease.

Cycle frequency of the duty cycle as output by the microcontroller 58and/or the operational switching frequency of the IGBT switch 62 maychange between the startup first-fourth phases P1-P4 and the steadystate fifth phase P5. For example, the cycle frequency may be at a firstfrequency during startup first-fourth phases P1-P4 and at a secondfrequency during steady state fifth phase P5. The first frequency may begreater than the second frequency. The first frequency may be at least10 kHz greater than the second frequency. The first frequency may beless than 20 kHz while the second frequency may be greater than 20 kHz.The first frequency may be 16 kHz while the second frequency may be 32kHz. The change in cycle frequency balances the heat production andresponsiveness of the algorithm for limiting current within motor 32.For example, a higher switching frequency is more responsive tocounteract increases in current through motor 32 but results in higherheat production within the switching components as they cycle at thehigher rate. Therefore, switching frequency is lower at the startupphases P1-P4 because higher current is needed through first-fourthphases P1-P4 (which generates greater heat) until motor 32 isaccelerated, at which point current through IGBT switch 62 is less and ahigher switching frequency in the steady state fifth phase 90 can betolerated despite increased heat production associated with higherswitching frequency.

The algorithm demonstrated in FIG. 3 for motor 32 startup and steadystate operation is particularly efficient at accelerating andmaintaining motor 32 speed while avoiding ring fire and overheating.This increase in efficiency allows motor 32 to be smaller, which isparticularly beneficial for a handheld unit that must be entirelysupported by the user.

The disclosed controller offers a number of advantages, includingincreased HVDC motor brush life, increased motor efficiency, eliminationof motor thermal trips, reduced motor heat rise, and variable sprayoutput.

The peak and RMS current can be controlled to a range below 4 Arms and7.3 A peak as would otherwise be typical in prior controllers usingtriac or SCR communication. This reduction in peak current and RMScurrent has two significant impacts that affect brush life. The firstpositive effect is reduced commutation arcing on the trailing edge ofthe brush between the brush and the rotating commutator bars. Thiseffectively reduces the electrical brush wear rate from that trailingarc causing the brushes to last longer in this application. High peakand RMS currents can cause excessively fast brush wear. The currentfeedback coupled with the PI loop used by microcontroller 58 helpsprevent excessive brush wear. The second effect is a reduction in brushheat rise and steady state operating temperature. Generally, with atemperature decrease, brushes have a lower coefficient of frictionduring operation which reduces the mechanical ware rate of the brush.Controller 38 can increase the amount of paint a user can spray beforereplacing the motor from 50 gallons of paint to more than 150 gallons,an increase of 200%.

With the addition of high voltage direct current power supply 50,current feedback circuit 66 and the PI loop used by microcontroller 58,the sprayer 10 is able to do the same amount of mechanical work but withlower RMS and peak current. With motor 32 operating at higherefficiency, less power is being wasted as heat and more is being usedfor work. This means paint sprayer 10 can utilize a smaller, lighterweight fractional horsepower motor taking up less space, reducingproduct weight and cost.

One significant issue with many paint spraying products is motor thermaltrips. A user will be spraying and the motor will overheat causing aninternal thermal fuse to open. A user then needs to wait 30 minutes forthe motor to cool down before the user can finish the painting job. Thishappens because different materials can cause the sprayer to work harderdue to their fluid properties. Some fluids increase the load on themotor and thus increase the peak and RMS currents the motor draws. Sincecontroller 38 increases the efficiency of the motor, less power iswasted as heat and more is used to do work. This allows for greaterloads to be applied the motor without significant variations in motorcurrent. With the addition of the current feedback loop and PIalgorithm, microcontroller 58 keeps the current below the maximumcontinuous current rating of motor 32. This means that no matter whatmaterials the user places in sprayer 10, controller 38 will adapt andlimit the power applied to motor 32 to ensure that motor is operatingwithin its designed limits.

The ability to provide a variable spray setting with spray setting input40 significantly enhances the spray performance for the user, reducingpaint waste due to overspray and limiting fluid flow dramatically for animproved finish in a wide range of materials and tip sizes. Thisvariable setting provides can provide a large number of different flowreduction operating points for the user.

The present disclosure is made using an embodiment to highlight variousinventive aspects. Modifications can be made to the embodiment presentedherein without departing from the scope of the invention. As such, thescope of the invention is not limited to the embodiment disclosedherein.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A fluid sprayer comprising: a housing; a pump connected to thehousing; a nozzle for spraying fluid delivered under pressure by thepump; a direct current brushed electric motor located in the housing andconfigured to operate the pump; and a motor controller electricallyconnected to the motor to drive the motor with a high speed pulse widthmodulated (PWM) signal that switches current through the motor on andoff.
 2. The fluid sprayer of claim 1 wherein the motor controller variesa duty cycle of the PWM signal as a function of a spray setting input.3. The fluid sprayer of claim 1, further comprising a current feedbackcircuit configured to sense current through the motor and generate acurrent feedback signal based on the sensed current through the motor,wherein the motor controller is configured to adjust a duty cycle of thePWM signal as a function of the current feedback signal.
 4. The fluidsprayer of claim 3, wherein the motor controller is configured to lowerthe duty cycle of the PWM based on the current feedback signalindicating that the sensed current through the motor exceeds apredetermined current level.
 5. The fluid sprayer of claim 1, whereinthe motor controller includes: a power supply that converts input ACpower to a DC voltage at a first motor terminal of the motor; asemiconductor switch having a first main current carrying electrodeconnected to a second motor terminal of the motor, a second main currentcarrying electrode, and a control electrode; a PWM driver that deliversthe PWM signal to the control electrode to cause the semiconductorswitch to turn on and turn off in response to the PWM signal; and; amicrocontroller that controls a duty cycle of the PWM signal.
 6. Thefluid sprayer of claim 5 wherein the motor controller further includes:a current feedback circuit connected to the second main current carryingelectrode for producing a current feedback signal representing sensedcurrent flow through the semiconductor switch; wherein themicrocontroller controls the duty cycle of the PWM signal as a functionof the current feedback signal.
 7. The fluid sprayer of claim 6, whereinthe microcontroller controls the duty cycle based upon a spray settinginput and the current feedback signal with a proportional-integral (PI)control loop.
 8. The fluid sprayer of claim 1, wherein the fluid sprayerincludes a trigger, and the motor controller controls whether the PWMsignal is delivered to the motor based on a status of the trigger. 9.The fluid sprayer of claim 1, wherein the fluid sprayer includes apressure transducer that measures fluid pressure and the motorcontroller controls whether the PWM signal is delivered to the motorbased on the measured fluid pressure.
 10. The fluid sprayer of claim 1,wherein the motor controller drives the motor with the PWM signal duringa start-up sequence phase of the motor, and drives the motor with thePWM signal during a steady state phase of operation of the motor, thesteady state phase following the start-up sequence phase.
 11. The fluidsprayer of claim 10, wherein the motor controller outputs the PWM signalto have a first switching frequency during the start-up sequence phaseand outputs the PWM signal to have a second switching frequency duringthe steady state phase, wherein the second switching frequency isgreater than the first switching frequency.
 12. The fluid sprayer ofclaim 10, wherein the start-up sequence phase includes a plurality ofphases of operation.
 13. The fluid sprayer of claim 12 wherein theplurality of phases includes a first phase in which the PWM signal has aduty cycle of greater than 85% and less than 100%.
 14. The fluid sprayerof claim 13 wherein the first phase has a duration of between 0.01 and2.0 milliseconds.
 15. The fluid sprayer of claim 13 wherein theplurality of phases includes a second phase that follows the firstphase, has a duty cycle that is less than the duty cycle in the firstphase, and has a duration of greater than 5 milliseconds and less than20 milliseconds.
 16. The fluid sprayer of claim 15 wherein the motorcontroller causes the duty cycle to ramp up during the second phase. 17.The fluid sprayer of claim 15 wherein the plurality of phases includes athird phase in which the duty cycle is constant and is less than theduty cycle in the first phase.
 18. The fluid sprayer of claim 17 whereinthe third phase has a duration of greater than 5 milliseconds and lessthan 20 milliseconds.
 19. The fluid spray of claim 10, wherein duringthe steady state phase the motor controller modulates the duty cycle ofthe PWM signal based upon a user selected pressure setting and ameasured parameter indicative of current through the motor.
 20. A methodof controlling power to a motor of a fluid sprayer, the fluid sprayercomprising a housing, a pump connected to the housing, a nozzle forspraying fluid delivered under pressure by the pump, the motor locatedwithin the housing and which operates the pump, a spray setting input, acurrent feedback circuit, and a motor controller, the method comprising:receiving a user selected pressure setting from the spray setting input;delivering a high speed pulse width modulated (PWM) signal whichswitches current through the motor on and off; measuring current throughthe motor with the current feedback circuit; and modulating a duty cycleof the PWM signal based on the user selected pressure setting and themeasured current through the motor.
 21. The method of claim 20, whereindelivering the PWM signal to the motor comprises delivering the signalthrough a start-up sequence in which the duty cycle of the PWM signal isfixed in a first phase and the duty cycle is lowered relative to thefirst phase in a second phase of the start-up sequence, and performingthe modulating step in a steady state phase of indefinite duration, thesteady state phase following the startup phase.